Dampers are used in vibration control applications to control resonance. One such application where dampers are commonly used is as a shock absorber for a vehicle suspension system designed to control ride and handling of a vehicle for the comfort and safety of its passengers.
There are several known types of suspension systems that have met with varying degrees of success. One such system is a conventional passive suspension, consisting of a passive spring and damper, which must compromise its ability to control a vehicle. Generally, low damping is preferred for good isolation of noise, vibration and harshness, whereas high damping is desired for control of body and wheel motion during cornering, acceleration and braking.
Another known type of suspension system is an adaptive suspension, which utilizes a passive spring and an adjustable damper with "slow" response to improve the control of ride and handling. The level of damping at all wheel positions can be selected by the driver, or it can be automatically tuned for variations in vehicle speed, steering angle, throttle position, brake pressure, or accelerometer signals.
Still another known type of suspension system is a semi-active suspension, which is similar to an adaptive suspension, except that the adjustable damper has "fast" response (less than 10 ms) and each wheel position is independently controlled in real time.
Yet another known type of suspension is a fully active suspension in which a hydraulic actuator is used in place of the damper to achieve better vehicle control but at a higher cost.
Theoretically, the performance of a semi-active suspension can approach that of a fully active suspension at a fraction of the cost. The preferred control algorithm, known as the "sky-hook" model, consists of a feed-back loop that adjusts damping level based on (1) the absolute vertical velocity of the vehicle body, and (2) the relative velocity between the body and the wheel.
A key component of this system is an adjustable damper with sufficiently fast response. One means of achieving variable damping is to use an electromechanical variable orifice to alter the flow resistance of a conventional hydraulic fluid. Another means is to use an electrically-charged fixed orifice to change the flow resistance of a field-responsive fluid such as electrorheological (ER) fluid.
The present invention relates to dampers that use suitable ER fluids for variable damping and which are intended ultimately to be incorporated in a semi-active suspension system. ER fluids, sometimes called "smart" fluids, are materials having flow properties that can be modified with electric field. This unique behavior may be utilized to adjust the damping force of dampers/shock absorbers with fast-acting electronic control by selectively applying voltage to the ER fluid.
Utilizing ER technology in damper applications offers advantages over conventional technology in that the ER effect is efficient, typically requiring only a few watts of electric power. Also, the damper construction is simplified due to the non-mechanical nature of ER technology, potentially decreasing manufacturing costs and increasing reliability. In addition, the ER effect provides the fast response needed for control of a complete semi-active suspension system which consists of several adjustable dampers/shock absorbers filled with ER fluid, power supplies to energize the fluid, sensors to provide feed-back, and a central command module.
The use of ER fluids in damper applications is generally known. However, there is a need for ER fluid dampers that provide an effective way of tuning the damping characteristics of the device to suit a particular application. Also, there is a need for an ER fluid damper package that is especially adaptable for use in an automobile suspension.